Load indicating member with identifying mark

ABSTRACT

A load indicating member is provided with a permanent identifying mark which can be read and used to determine ultrasonic measurement parameters specific to the load indicating member to provide more precise and more reliable load measurements by compensating for differences resulting from manufacturing variations in individual load indicating members. The parameters specific to the load indicating member can be stored in coding applied to the load indicating member or in a database that can be accessed remotely, for example, using the Internet.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/264,877, filed Jan. 29, 2001.

BACKGROUND OF THE INVENTION

This invention relates to load indicating members and, moreparticularly, to load indicating members, such as fasteners, havingultrasonic transducers.

In many operations, it is desirable to determine the amount oflongitudinal load experienced by a longitudinally stressed member. Thisinformation is particularly useful when the longitudinally stressedmember is a fastener since the measurement of longitudinal load providesa verification of the existence of a proper joint.

Ultrasonic load measurement is a precise measurement technique fordetermining load in bolted joints. Pulse-echo techniques with removableultrasonic transducers have been used in laboratories and for qualitycontrol for over thirty years. Historically, however, the practicaldifficulties in achieving reliable acoustic coupling and inincorporating transducers in tool drives have prevented this techniquefrom becoming a general assembly tightening strategy.

The above coupling difficulties were overcome with permanently attachedtransducers. U.S. Pat. No. 4,846,001 (issued to Kibblewhite) teaches theuse of a thin piezoelectric polymer film which is permanently,mechanically, and acoustically coupled to an end surface of a member andused to determine the length, tensile load, stress or other tensileload-dependent characteristic of the member by ultrasonic techniques.Although the invention represented a significant advance over the priorstate of the art in terms of performance, ease of manufacture, andmanufacturing cost, there are disadvantages with a transducer of thisconstruction. These disadvantages relate to environmental performance,in particular the maximum temperature limitations of the polymermaterial which restricts its application, and the possibility of thetransducer, fixed to the fastener with adhesive, coming loose andcausing an obstruction in, or damage to, a critical assembly.

U.S. Pat. No. 5,131,276, issued to Kibblewhite and assigned toUltrafast, Inc., teaches a load-indicating member having an ultrasonictransducer, including an acousto-electric film, grown directly on thefastener surface (i.e., a piezoelectric thin-film). By growing theacousto-electric film directly on the fastener, the film ismechanically, electrically, and acoustically interconnected to thesurface. Permanent ultrasonic transducers not only allow the precisepulse-echo load measurement technique to be used in production assemblybut also significantly improve accuracies by eliminating errors thatresult from axial and radial movement of the removable transducerrelative to the bolt and from variations in the coupling media.

All the above-mentioned ultrasonic methods of determining load in a loadindicating member require a zero-load measurement in addition to themeasurement taken under the desired loaded condition in order todetermine the absolute load in the member. Furthermore, all use a director indirect measurement of the out-and-return time-of-flight of alongitudinal ultrasonic wave. Holt, U.S. Pat. No. 4,602,511, teaches ofa method which uses the times-of-flight of both longitudinal andtransverse waves to determine the stress in a member without taking azero-load measurement. This is desirable in the measurement of tensileload in previously installed fasteners, for example.

The use of transverse ultrasonic waves, however, requires both atransducer capable of generating transverse waves and an acousticcoupling media capable of transmitting transverse waves into the member.Special acoustic couplants are required with temporarily attachedtransducers, since transverse waves cannot generally be transmittedthrough liquids. Although adhesives can transmit transverse ultrasonicwaves, generation of transverse waves using the polymer film transducersdisclosed by Kibblewhite in U.S. Pat. No. 4,846,001 has not beendemonstrated. Only the permanent ultrasonic transducer technologydisclosed by Kibblewhite in U.S. Pat. No. 5,131,276 has demonstrated apractical method of making load measurements in fasteners without firsttaking a zero-load measurement using the method based on measurements ofboth longitudinal and transverse waves. However, accuracies of only ±15%are typically achievable with this method due to production variationsin the material and geometry of the fasteners.

The above-mentioned ultrasonic load measurement methods usinglongitudinal waves alone are capable of precise measurements when azero-load measurement is made prior to tightening, with typicalaccuracies of ±3% documented. Because of the variation in initiallengths of fasteners manufactured using production methods, measurementof installed load at a later time is only possible with ultrasonic loadmeasurements using longitudinal waves alone by recording the zero-loadlength measurement. Ultrasonic load measurement instruments have theability to store and retrieve zero-load measurements for laterinspection of load.

A means of identifying each fastener for storing and retrievingzero-load length measurements with removable transducer ultrasonic loadmeasurement instrumentation is disclosed by Shigemi et al. in JapanesePatent Application Publication No. 10-086074. Shigemi discloses a methodof applying an identifying mark, such as a bar code, on the periphery ofthe head of the fastener. The bar code is read by an optical bar codereader and the zero-load ultrasonic length measurement is stored inmemory in a control device corresponding to the identifying mark on thefastener. When reading the fastener load at a later date, theidentifying mark is first read to retrieve the zero-load lengthmeasurement. Zero-load bolt length is the only ultrasonic parameterassociated with a specific bolt disclosed by Shigemi. Also, the bar codedisclosed by Shigemi is used for identification purposes only andcontains no encoded ultrasonic measurement information. While thisinvention is suitable for a single instrument at a single location,storing and retrieving a zero-load length alone is inadequate inensuring reliable precise measurement with all fastener types, withdifferent instruments or with different ultrasonic transducers, such asat multiple service locations, for example.

A difficulty in making reliable fastener load. measurements withultrasonic pulse-echo instrumentation arises from the uncertainty inconsistently identifying the same echo cycle to which time-of-flightmeasurements are made. Considerable distortion of the echo waveform canoccur, especially with fasteners with large length-to-diameter ratios,primarily due to fastener geometry and stress distribution variations.Vecchio et al., in U.S. Pat. No. 6,009,380, disclose a multi-frequencyexcitation and detection method to improve the reliability of detectingthe correct echo cycle when making ultrasonic time-of-flightmeasurements for determining fastener load. The method storescharacteristics of a typical echo waveform as a reference for aparticular fastener type. However, variations in echo waveforms fromfasteners of the same type can be sufficiently large to prevent thismethod,.using a single reference for a particular fastener type, fromworking reliably for all fasteners. Consequently, fasteners whichdeviate significantly from the reference waveform characteristics areunsuitable for reliable inspection with this method and must be screenedout in production.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a practicalmethod of storing a complete ultrasonic signature for individualhigh-volume production fasteners in a manner that can be retrieved at alater time by different instrumentation at different locations forreliable precise load measurement for verification of joint integrity.

A further object is to provide a low-cost, permanent, durable mark, suchas a high-density bar code, that can be applied to load indicatingfasteners, for uniquely identifying individual fasteners.

Another object is to provide an easily accessible database for storingand retrieving fastener ultrasonic signatures, historical tighteningdata and load data for individual high-volume fasteners.

Yet another object is to provide a low-cost, permanent, durable mark,such as a high-density bar code, that can be applied to load indicatingfasteners, capable of storing all the ultrasonic load measurementparameters, unique to a particular fastener, within the code.

Yet another object is to provide a marking system which is practical foruse with permanent ultrasonic transducers on fasteners.

Yet another object is to provide a single instrument which automaticallyidentifies a load indicating fastener, retrieves the ultrasonicmeasurement parameters for the fastener, measures the pulse-echotime-of-flight of an ultrasonic wave, measures the temperature of thefastener and precisely and reliably determines the load in the fastener.

Yet another object is to provide a method of bonding an ultrasonictransducer to a load indicating member using a chemical grafting method.

Yet another object is to provide a load indicating member with apermanent ultrasonic transducer including a magnetic recording materialfor storing and retrieving data.

Yet another object is to provide a high-density bar code label suitablefor use in identifying parts subject to high temperature and corrosiveenvironments.

The present invention eliminates many of the disadvantages of loadindicating members of the prior art and provides additional features andadvantages not previously available in load indicating members, loadindicating fasteners, load indicating devices and tightening tools.

The load indicating member of the present invention has a permanentidentifying mark which can be read and used to determine ultrasonicmeasurement parameters specific to the load indicating member to providemore precise and more reliable load measurements by compensating fordifferences resulting from manufacturing variations in individual loadindicating members.

In a preferred embodiment of the present invention, a load indicatingmember has an ultrasonic transducer, permanently mechanically,electrically and acoustically attached to one end of the load indicatingmember, such that the load indicating member functions as a firstelectrode. The ultrasonic transducer comprises a piezoelectric element,adjacent to the end surface of the load indicating member, and anelectrically conductive layer adjacent to the piezoelectric element,functioning as a second electrode. A high-density two-dimensionaloptically-read bar code is permanently marked on the surface of theelectrode. In this embodiment, the bar code stores not only a uniqueidentification of the load indicating member but also all of theultrasonic parameters, specific to that load indicating member, requiredto make precise, reliable load measurements.

One method of making the load indicating member of the preferredembodiment of the present invention includes the steps of providing theload indicating member with its permanently attached ultrasonictransducer, measuring the ultrasonic measurement parameters and markinga bar code, in which the ultrasonic measurement parameters are encoded,on the top electrode of the transducer.

An alternative method of making the load indicating member of thepresent invention includes the steps of providing the ultrasonictransducer, comprising the piezoelectric element and electrode layer onwhich is marked a unique identifying bar code, permanently attaching anultrasonic transducer to the load indication member, measuring theultrasonic measurement parameters and storing the ultrasonic measurementparameters in a database associated with the unique identifying barcode.

A method of measuring the load in a load indicating member of thepresent invention includes the steps of reading the bar code with anoptical reader, determining the ultrasonic measurement parameters,making pulse-echo time-of-flight ultrasonic wave measurements, andcalculating the precise load.

In another embodiment of the present invention, the permanent mark isapplied directly to the load indicating member, and the ultrasonicmeasurements are made with a removable ultrasonic transducer temporarilyattached to the load indicating fastener.

The high-density bar code of the present invention can be marked eitherwith an inkjet marking system or, preferably, using a laser markingsystem. In an alternative embodiment, a dot code mark is made bydrilling holes through the top surface layer with a laser to form thebar code.

The present invention further includes a database of ultrasonicmeasurement parameters and historical loading data corresponding to eachload indicating member, such database being readily interconnected withmeasurement instruments over a computer network, such as the Internet,and preferably in a manner transparent to the measurement equipmentoperator.

The present invention further includes an estimation of the load in aload indicating member which has been elongated beyond its yield pointduring a loading operation, based on the historical loading data forthat load indicating member.

In yet another embodiment of the present invention, a high-density barcode is permanently marked on a thin, durable corrosive-resistant foiland attached to a part as a label for identification purposes.

In yet another embodiment of the present invention, the top electrode ofthe permanent ultrasonic transducer on the load indicating member ismade of a magnetic recording material, such as a nickel cobalt alloy,for example, and the bolt identification, ultrasonic measurementparameters and tightening data are stored and read with magneticrecording and reading devices.

In yet another embodiment of the present invention, chemical grafting isused to permanently bond the layers of film or foil to form a permanentultrasonic transducer on a load indicating member or a permanentidentifying mark on a part.

It is to be understood that both the foregoing summary description andthe following detailed description are exemplary, but not restrictive,of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following drawings, like reference numerals refer to likeelements throughout.

FIG. 1 is a perspective view of a load indicating member according tothe present invention.

FIG. 2 is a partial view of a load indicating member according to thepresent invention.

FIG. 3 is a top view of the top electrode of the load indicating memberof FIG. 1.

FIG. 4 is a perspective view of an alternative example of a loadindicating member according to the present invention.

FIG. 5 is a top view of the top electrode of the load indicating memberof FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

A number of measurement parameters are required to determine tensileload, stress, elongation or other measure indicative of tightness of aload indicating member, such as a bolt, rivet or rod, from ultrasonicpulse-echo time-of-flight measurements. These parameters are specific tothe load indicating member, the joint in which the load indicatingmember is installed, the ultrasonic transducer used to transmit andreceive the ultrasonic waves and the instrumentation used to make thetime-of-flight measurements. These parameters are used to make reliableultrasonic measurements and determine the relationship between theultrasonic time-of-flight measurements and load, stress or elongation,and are influenced by, for example, the material, diameter and length ofthe load indicating member, the effective length on the clamped jointcomponents, the transducer acousto-electric characteristics andinstrumentation timing delays. Many of these influences are effectivelyconstant for a specific type of load indicating member and joint, andmeasurement parameters affected solely by these can be predetermined fora specific joint, stored in the measurement instrumentation and selectedat the time of measurement. There are, however, certain parameters thatvary with each specific load indicating member due to variations intheir manufacturing tolerances. These include, for example, the preciselength of the bolt, acoustic properties of the material, internalresidual stresses and, in the case of a permanently attached ultrasonictransducer, the acousto-electric characteristics of the transducer.

When a load indicating member, such as a fastener, is being installedfrom a known zero-load condition, the parameters needed to compensatefor these variations can be determined and used during the loadingoperation. However, in order to make equally precise load measurementsat a later date, for example, measuring the load in pre-installedfasteners, there needs to be a practical way to store and retrieve theparameters specific to each load indicating member. This is provided inaccordance with the present invention as follows.

Referring now to the drawings, and more particularly to FIGS. 1, 2 and 3thereof, a first embodiment of a load indicating member, and moreparticularly, a load indicating fastener 10 is described. Loadindicating fastener 10 is a fastener with a permanent piezoelectricpolymer film transducer attached to one end, an example of which isdisclosed in U.S. Pat. No. 4,864,001 issued to Kibblewhite, andincorporated by reference herein. The load indicating fastener of thepresent invention further includes a two-dimensional high-density barcode 12 on top electrode 14 of permanent ultrasonic transducer 16.

The load indicating fastener 10 is formed from a conventional bolt whichhas been modified to provide an indication of the tensile load, stress,elongation or other characteristic of the bolt during a tighteningoperation, as well as at various other times during the life of a joint.A thin piezoelectric polymer sensor 18 is permanently, mechanically andacoustically attached to end surface 20 of the bolt. In this embodiment,the piezoelectric polymer sensor 18 is a 9 micron thick, polyvinylidenefluoride copolymer film, manufactured by Measurement Specialties Inc.,Valley Forge, Pa.

In this first embodiment of the present invention, top electrode 14 is athin metallic foil, specifically approximately 50 micron thick, type316, full-hard, dull or matte finished stainless steel, which has beentreated to provide a black oxide finish. The stainless steel isavailable as conventional shim stock which can be specified with arolled dull or matte finish, or alternatively, chemically treated toprovide a dull or matte finish. The black oxide treatment provides anextremely thin (less than 0.5 micron), durable, corrosion resistant,electrically conductive, black coating. A durable, high-resolution barcode can be marked on this surface by removing selected areas of thecoating, by conventional laser ablation techniques known in the art, toprovide a high contrast mark easily read with conventional, commerciallyavailable optical readers.

In this first embodiment, the method of making the load indicatingmember 10 of the present invention includes the steps of providing aflat surface 20 on one end of the fastener, bonding piezoelectric film18 to the black oxide coated stainless steel, cutting a 6 mm diameterdisc of polymer/stainless steel laminate, bonding the disc to flatsurface 20 such that the polymer is adjacent flat surface 20 and thestainless steel foil forms the top electrode 14 of ultrasonic transducer16, measuring the ultrasonic measurement parameters specific to the loadindicating member with ultrasonic pulse-echo instrumentation while theload indicating fastener is at zero-load, encoding measurementparameters and a unique identification into a bar code and permanentlymarking the bar code 12, with a laser, on the surface of the topelectrode 14.

The type of bar code used in this first embodiment is preferably ahigh-density, two-dimensional code known as a “GoCode”, which is aproprietary product of the Gocode Product Corporation, Draper, Utah.This code format provides the ability to store 34 alphanumericcharacters on the 6 mm diameter stainless steel top electrode. As willbe appreciated by one skilled in the art, there exist many alternativetwo dimensional bar code formats which could be used to store this data.

In a similar second embodiment of a load indicating member of thepresent invention, only a unique identification is encoded in bar code12, and the ultrasonic measurement parameters associated with loadindicating member 10 with this unique bar code are stored in a database,rather than encoded in the bar code itself. Since the data itself is notencoded within the code, unique bar codes can be marked on the stainlesssteel foil prior to cutting the disc and bonding it to the fastener toform the load indicating member. In this embodiment, the loadmeasurement instruments require the data from the load measurementparameter database in order to make a load measurement in apre-installed fastener.

An alternative method of providing a permanent durable bar code on thestainless steel of the top electrode is illustrated in FIGS. 4 and 5. Adot-type bar code 30, such as the proprietary “Snowflake” code availablefrom Marconi Data Systems, Wood Dale, Ill., is marked on top electrode32 with holes 34 laser drilled through the foil. Since typically lessthan 150 10 micron diameter holes are required for the code, theirpresence has an insignificant effect on the acousto-electric performanceof the transducer.

In a third embodiment of the present invention, a load indicating memberof the type disclosed in U.S. Pat. No. 5,131,276 (Kibblewhite),incorporated by reference herein, is provided in which a piezoelectricthin-film transducer is grown directly on one end of a fastener by avacuum deposition method, such as magnetron sputtering. Alternatively, aload indicating member is provided in which a piezoelectric thin-filmtransducer is grown directly on foil by a vacuum deposition method, suchas magnetron sputtering, and the transducer is then mechanically,electrically and acoustically attached to the fastener. Also provided isa surface on the top electrode, or elsewhere on the load indicatingmember, suitable for the marking of a bar code with the above-describedmarking methods, to provide the same function as those of theabove-described embodiments of the present invention. Alternatively, anadditional, thin color-contrasting layer could be vacuum depositedduring the manufacturing operation. Parts of this layer could then beselectively removed by laser ablation, in a manner similar to thatdescribed above for the stainless steel black oxide layer, to mark thehigh-density bar code.

In an alternative embodiment of the present invention for use withremovable ultrasonic transducers temporarily attached to a fastener, thepermanent mark is applied directly to the fastener. The high-density barcode is marked on the fastener after zero-load ultrasonic measurementsare made on the fastener and, as with the above-described firstembodiment of the present invention, contains encoded fastener-specificultrasonic measurement parameters. Consequently, load in the bolt can beread by different instruments and at different locations, such asservice locations, without access to a database of fastener-specificultrasonic measurement parameters. The bar code is marked on thefastener with one of the above-described methods.

It will be appreciated by one skilled in the art that there arealternative constructions of the ultrasonic transducer of the presentinvention. The ultrasonic transducer can be placed on a flat surface ina recess or at the bottom of a hole, for example, with internal drivefasteners. Alternative materials and thicknesses for the top electrodeand for the piezoelectric element are possible, and can be selected toproduce the desired durability, environmental resistance andacousto-electric performance for a particular application. Additionally,alternative piezoelectric materials, including ceramic piezoelectricmaterials, can be used and the piezoelectric material can be coated withthin electrically conductive layers to enhance acousto-electricperformance. Alternative thicknesses of the piezoelectric element canalso be used. Alternative bar code marking methods, such as inkjetmarking, laser marking which heats the surface to discolor the material,and the use of laser-activated or laser-bonded coatings can be used withthe present invention. Alternatively, also in the above-describedembodiments, the bar codes could be marked directly on the fastener orin the vicinity of the fastener. It will be appreciated by one skilledin the art that the above-described embodiments of the present inventioncan be used with load indicating members using both longitudinal andtransverse waves, such as those described by Kibblewhite in U.S. Pat.No. 4,846,001, and with load indicating fasteners provided withultrasonic reflecting surfaces, such as annular groves, as disclosed byKibblewhite in U.S. Pat. No. 5,029,480.

For those embodiments of the present invention in which the measurementparameters are encoded directly in the bar code, the method of measuringthe load in a pre-installed load indicating member includes the steps ofreading the bar code with an optical reader, decoding the bar code toretrieve the ultrasonic measurement parameters, making pulse-echotime-of-flight ultrasonic wave measurements, measuring a temperatureindicative of the temperature of the load indicating member, andcalculating the precise load.

For those embodiments of the present invention in which the bar code issolely a unique identification of the load indicating member, the methodof measuring the load in a pre-installed load indicating member includesthe steps of reading the bar code with an optical reader, decoding theunique identification of the load indicating member, retrieving theultrasonic measurement parameters associated with that unique bar codefrom a database, making pulse-echo time-of-flight ultrasonic wavemeasurements, measuring a temperature indicative of the temperature ofthe load indicating member, and calculating the precise load.

When measuring load in a load indicating member of the present inventionduring an assembly operation when a recently measured zero-loadtime-of-flight measurement is available, a measure of temperature is notrequired, since the change in temperature of the load indicating memberduring the assembly operation is small and typically has aninsignificant effect on load measurements.

Assembly tools for use with load indicating fasteners are known in theart and are described by Kibblewhite in U.S. Pat. No. 4,846,001. Suchtools are typically standard tools modified to take ultrasonic loadmeasurements during tightening, to compare these measurements with apredetermined desired load, and to stop the tightening process byturning off the tool when the desired load is reached. If such tools arededicated to a specific fastener type, such as on an automotive assemblyline, for example, and are tightening from a zero-load condition, theirassociated controls can be preset with the ultrasonic measurementparameters specific to the fastener type and, therefore, do not requirea bar code reading device.

A load inspection device of the present invention includes a bar codereading device, an ultrasonic pulse-echo time-of-flight measurementdevice, a device for inputting or measuring a temperature indicative ofthe temperature of the fastener, and a device for calculating load forrecording or display. Preferably, the devices for measuring the barcode, the ultrasonic time-of-flight and the temperature are.incorporated in a single probe to provide a simple, efficientmeasurement device.

In the present invention, ultrasonic measurement parameters andhistorical loading data corresponding to each load indicating member areuploaded to a database. The database is readily interconnected withmeasurement instruments over a computer network, such as the Internet,preferably in a manner which is transparent to the measurement equipmentoperator. The ultrasonic measurement parameters recorded during themanufacture of the load indicating member are stored in the database.During tightening of the load indicating member with an assembly tool,loading data recorded by the load measurement instrumentation is alsouploaded to the database. The database, therefore, contains a completerecord of the loading history of the fastener. A fastener loadinspection device connected to the database can, for example, not onlyprecisely measure the load in a fastener, but also indicate the drop inload since that fastener was installed. This information is useful inautomotive and aerospace preventative maintenance operations.

It will be appreciated by one skilled in the art that the data bothencoded in the bar code and stored in the database can be structured tominimize the size of the data records to be stored and transferred. Forexample, data common to a particular fastener type need only be storedonce, and individual fastener bar codes or database records wouldrequire only a reference index to this data, such as a fastener partnumber, plus data specific to the individual fastener.

Ultrasonic load measurements using longitudinal waves can only measureload accurately in fasteners up until the yield point, since beyond thatpoint the elongation is no longer elastic and permanent plasticelongation takes place. The ultrasonic load measurement method whichuses both longitudinal and transverse wave times-of-flight, disclosed byHolt in U.S. Pat. No. 4,602,511 can, in theory, measure load beyondyield, but is subject to significant errors resulting from the effect ofyielding on residual stresses within the fastener. In the presentinvention, loads beyond yield are estimated from a typical increase intime-of-flight verses yield characteristic for the specific fastenertype, determined experimentally and stored in the database. Furthermore,since the complete loading history for each fastener is maintained inthe database, drop in load can be determined precisely from differencesbetween the maximum time-of-flight measurement recorded for the fastenerand its then current time-of-flight.

In the above-described embodiments of the present invention, the bondingof the top electrode layer to the piezoelectric polymer 18 and thebonding of the piezoelectric polymer 18 to the top surface 20 of bolt 10can be accomplished using an adhesive, such as an epoxy adhesive.Alternatively and preferably, this is accomplished with a process knownas chemical grafting, such as that developed by the Polymer ResearchCorporation of America, Brooklyn N.Y., and described in their ProductBulletin entitled “Insuring your Products Future through ChemicalGrafting”. Chemical grafting uses an activator to produce a strongcovalent chemical bond, rather than a physical bond. The processinvolves the activation, attachment and polymerization using amaterial-specific graft initiator-monomer system. The process can bevisualized as a growth of “whiskers” onto the substrate. These whiskersattach themselves at activation sites forming polymer chains linked bycovalent bonds. Chemical grafting produces such a strong bond that thematerials rupture before the bond is broken. The use of chemicalgrafting, therefore, eliminates the disadvantage of the inventiondisclosed by Kibblewhite in U.S. Pat. No. 4,889,591, that the transducercan come off the load indicating member during the life of the productin which it was installed.

In yet another alternative embodiment of the present invention, a loadindicating member with a permanent ultrasonic transducer uses a magneticrecording media as the material for its top electrode. Such a topelectrode is manufactured from one of a number of electricallyconductive magnetic materials, such as nickel or cobalt alloys and thoseused for aircraft flight recorders, for example. Data is recorded andread by inductive read/write heads similar to those commonly used in,for example, computer magnetic disks, audio and video recorders andmagnetic strip readers. An advantage of this embodiment of the presentinvention is that the data, such as the ultrasonic measurementparameters, unique identification number and tightening data can berewritten, appended to or updated by the measurement instruments.

The metal foil with the bar code marking, used for making the topelectrode of some embodiments of the present invention, provides anextremely durable, corrosion and temperature resistant, permanent barcode label or tag and, therefore, this element itself can be used touniquely identify a component or store a permanent record of criticaldata associated with an object in applications other than loadindicating members. Such applications include the identification ofaircraft parts and medical record tags, for example. When used as alabel, the foil can be bonded to a component with an adhesive or byusing the above-described chemical grafting.

1. An apparatus comprising: an ultrasonic transducer coupled with anobject, for making ultrasonic measurements in the object; andinformation storage means on the ultrasonic transducer, wherein theinformation storage means includes markings corresponding to dataassociated with the object.
 2. The apparatus of claim 1 wherein theobject is a fastener, and wherein the ultrasonic transducer is attachedto the fastener for making measurements indicative of load in thefastener.
 3. The apparatus of claim 1 wherein the ultrasonic transduceris permanently attached to the object.
 4. The apparatus of claim 1wherein the ultrasonic transducer is temporarily attached to the object.5. The apparatus of claim 1 wherein the information storage means is anoptical storage media.
 6. The apparatus of claim 5 wherein the opticalstorage media is a color-contrasting mark provided on an exposed surfaceof the ultrasonic transducer.
 7. The apparatus of claim 5 wherein theoptical storage media is a reflectivity-contrasting mark provided on anexposed surface of the ultrasonic transducer.
 8. The apparatus of claim5 wherein the optical storage media is a bar code.
 9. The apparatus ofclaim 8 wherein the bar code is a two-dimensional bar code.
 10. Theapparatus of claim 5 wherein the ultrasonic transducer has anelectrically-conductive layer, and wherein the optical storage media isapplied to the electrically-conductive layer.
 11. The apparatus of claim5 wherein the optical storage media is a laser-etched marking.
 12. Theapparatus of claim 5 wherein the optical storage media is acontrast-enhancing coating.
 13. The apparatus of claim 5 wherein theoptical storage media is a black-oxide coated surface of a metallic foilincluding portions of the black-oxide coating which are selectivelyremoved by laser ablation.
 14. The apparatus of claim 5 wherein theoptical storage media is a foil including holes drilled through thefoil.
 15. The apparatus of claim 1 wherein the information storage meansis a magnetic storage media, and wherein the magnetic storage mediaincludes a layer of magnetic material capable of storing data.
 16. Theapparatus of claim 1 wherein the information storage means contains thedata associated with the object.
 17. The apparatus of claim 1 whereinthe information storage means contains a marking for identifying theobject.
 18. The apparatus of claim 17 wherein the marking foridentifying the object is coupled with an index in a database whichcontains data relating to the object.
 19. The apparatus of claim 18wherein the database is accessible over the Internet.
 20. The apparatusof claim 1 wherein the information storage means contains the dataassociated with the object and a marking for identifying the object. 21.The apparatus of claim 1 wherein the object is a fastener, and whereinthe data includes a zero-load acoustic length of the fastener.
 22. Theapparatus of claim 1 wherein the object is a fastener, and wherein thedata includes parameters for deriving a zero-load acoustic length of thefastener.
 23. The apparatus of claim 1 wherein the object is a fastener,wherein the data includes an acoustic signature of the fastener, andwherein the acoustic signature contains parameters for deriving anultrasonic echo waveform measurement cycle for the fastener.
 24. Theapparatus of claim 1 wherein the object is a fastener, and wherein thedata includes parameters relating to the fastener for calculating loadin the fastener from the ultrasonic measurements.
 25. The apparatus ofclaim 1 wherein the object is a fastener, and wherein the data includesparameters relating to a joint into which the fastener is tightened, forcalculating load in the fastener from the ultrasonic measurements. 26.The apparatus of claim 1 wherein the object is a fastener, and whereinthe data includes a parameter relating to the fastener which is measuredduring tightening of the fastener.
 27. The apparatus of claim 1 whereinthe object is a fastener, and wherein the data includes a parameterrelating to the fastener which is measured during subsequent loading ofthe fastener.
 28. The apparatus of claim 1 wherein the object is afastener, and wherein the data includes a parameter relating to thefastener which is measured to determine changes in loading of thefastener.
 29. The apparatus of claim 28 wherein acoustic length ismeasured to determine permanent elongation of the fastener.
 30. Theapparatus of claim 1 wherein the information storage means are applieddirectly to the ultrasonic transducer.
 31. The apparatus of claim 1wherein the information storage means are integral with the ultrasonictransducer.
 32. The apparatus of claim 1 wherein the information storagemeans are provided on a surface of the ultrasonic transducer.